Process and device for drawing off and blocking off a melt

ABSTRACT

Process and device for drawing off and blocking off a melt, especially of plastic material, with a heatable melter (1) fitted with a blocking valve (3) acting as a melt distributor from which the melt flows into a nozzle plate (10) which divides the melt by means of nozzles (14) into a plurality of threads, whereby the temperature of the melter and nozzle plate is regulated separately and the blocking valve is closed to block the melt off and the nozzle plate is tightly closed off by a cover (18). To draw off the melt with the blocking valve open, the temperature of the melter and the nozzle plate is kept substantially at the same level and to block off the melt with the blocking valve closed the nozzle plate is taken to a temperature just above the solidification temperature of the melt material. With the closure of the blocking valve the cover, which is cooled to a temperature considerably below the solidification temperature, is laid on the nozzle plate into which residual melt flows and seals off the nozzle apertures in the solidified state.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a process and a device for drawing off andblocking off a melt, in particular of plastic material, with a heatablemelter, which is provided with a blocking valve and acts as a meltdistributor and from which the melt flows into a nozzle plate, whichdivides the melt by means of nozzles into a plurality of strands,whereby the temperature of the melter and nozzle plate is regulatedseparately and the blocking valve is closed to block off the melt, andthe nozzle plate is tightly closed off by a cover.

It is necessary to seal off the melt at the nozzle apertures if the meltflow is blocked off, in order to prevent the air from penetrating fromthe nozzle apertures; said air can trigger an oxidation process of themelt, which leads to an undesired chemical change in the melt material.To date the cover used for this closure was usually screwed to thenozzle plate. It is thereby necessary that the cover rests withsignificant pressure on the nozzle plate, in order to obtain therequisite sealing effect. It has turned out that apparently owing to theexisting temperature differential a distortion of the cover isinevitable, a feature that results in the nozzle apertures being sealedonly incompletely and thus the air having access.

The object of the invention is to improve the seal of the nozzleapertures in the case of the melt flow being blocked off. According toinvention this problem is solved in that to draw off the melt with theblocking valve open, the temperature of the melter and the nozzle plateis kept substantially at the same level, and to block off the melt withthe blocking valve closed the nozzle plate is lowered to a temperaturejust above the solidification temperature, and with the closure of theblocking valve the cover cooled to a temperature considerably below thesolidification temperature is laid on the nozzle plate into which aresidual melt flows and seals off the nozzle apertures in the solidifiedstate.

The temperature in the melter and the nozzle plate that is kept at thesame level while drawing off the melt is changed in such a manner whenblocking off the melt flow that, while the temperature in the melter iskept unmodified, the temperature level in the nozzle plate is lowered,and in particular so far that in the nozzle plate a temperature justabove the solidification temperature of the melt material prevails. Ifthen owing to the considerable cooling of the cover, the coveraccommodating the melt material converts the melt material into thesolidified state, the solidified material can seal off the nozzleapertures, and in particular also permanently, since owing to thelowering of the temperature in the nozzle plate, the solidified meltmaterial held by the cover cannot be melted again from that direction.The result is thus, owing to the solidified melt material a reliablesealing of the nozzle apertures, thus reliably preventing the air frompenetrating and thus oxygen into the region of the melt. This kind ofsealing of the nozzle plate also allows the cover to be laid with lessprecision on the nozzle plate, without requiring a specific pressure tothis end, since the necessary seal is brought about not by the coveritself but, as said, by the solidified melt material.

The device to effect the process described above is based on a heatablemelter, which is provided with a blocking valve and which is acting as amelt distributor and to which is attached a nozzle plate, which dividesthe melt into a plurality of strands by means of nozzles and which canbe sealed off with a cover. This device is designed in such anadvantageous manner that the nozzle plate and the cover are providedwith one separate and individually controllable heating or coolingsystem each, whereby between the melter and the nozzle plate atemperature insulating layer, which connects sealingly melter and nozzleplate, is installed, and the cover exhibits a recess, extending over thenozzle apertures, as the collecting basin for the melt cooled by thecover.

The recess in the cover, which serves as the collecting basin for themelt cooled by the cover, can be relatively flat, so that a relativelythin layer is formed by the solidified melt material in the recess. Thisis totally adequate for the sealing effect. In so doing, the temperatureinsulating layer provided between melter and nozzle plate provides thatthe temperature prevailing in the melter has no effect on thetemperature in the nozzle plate that is cooled in contrast.

If the melt is to be drawn off again from the device, the cover isremoved from the nozzle plate. Depending on the melt material used, thecover can take along in its recess the solidified melt layer. In thiscase the cover can be provided with a ram penetrating the cover in theregion of its recess, in order to push out the solidified melt material.With the cover removed, the ram is pushed forward, whereby thesolidified melt layer drops out of the recess of the cover.

The cover can be affixed or removed by hand, but it is also possible tocarry out this procedure, e.g., with a swivel or slide mechanism. In sodoing, it is especially advantageous that the cover does not constitutea risk for the operating personnel on account of its cooling.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures show embodiments of the invention.

FIG. 1 is in principle a sectional view of a melter with nozzle plateand cover laid on the nozzle plate.

FIG. 2 is a modified design with a cover that can be swivelled withrespect to the nozzle plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a device to draw off and block off a melt, in particular ofplastic material, with a melter 1, to which is fed plastic melt by meansof a feed line 2. The blocking valve 3 is laid into the feed line 2. Themelter 1 is enveloped by a heating chamber 4, which encloses said melterlike a ring and into which a heating liquid flows through the inlet 5and flow out of said heating chamber through the outlet 6. Thetemperature of the melter is measured continuously by means of atemperature probe 7. The melter 1 is enveloped by an insulating casing8, shown in the drawing with cross hatching, for the purpose ofpreventing heat loss. The melter has the interior 9, which is filled bymelt and which expands correspondingly in the direction of the nozzleplate 10 to be attached.

The temperature insulating layer 12, which connects sealing the face 11of the melter with the side of the nozzle plate 10 concerned, is affixedto the flat face 11 of the melter 1. The temperature insulating layerserves to prevent a direct heat transfer from the melter 1 to the nozzleplate 10.

The nozzle plate 10, which is penetrated by channels 13, which terminatein the nozzles 14, follows the temperature insulating layer 12. If themelt is drawn off, the melt flows through the inner chamber 9 of themelter 1 through the channel 13 and exits on the bottom side of thenozzle plate 10 out of the nozzles 14. The nozzle plate 10 is connectedby means of inflow 15 and outflow 16 to a heating and cooling mediumstream for which channels extending in a ring around the nozzle plate 10are provided. By means of the medium flowing through the channels 17,the nozzle plate 10 is kept at the desired temperature level.

On the bottom side of the nozzle plate 10 rests the cover 18, whichextends with its recess 19 over all nozzles 14. Thus, the drawing inFIG. 1 shows the operating phase in which the melt stream is blockedoff. The cover 18 exhibits the channel 20, which extends over the entirelength of said cover and which is attached to a coolant stream by meansof the inlet 21 in the outlet 22. With the aid of this coolant the cover18 can be raised to a temperature considerably below the temperature ofthe nozzle plate 10.

According to the process step described in the introductory part, thecover 18 has been laid on the nozzle plate 10 together with the closureof the blocking valve 3, so that only a residual melt can penetrate outof the inner chamber 9 of the melter 1 into the recess 19. This residualmelt solidifies owing to the considerable cooling of the cover 18relative to the nozzle plate 10, so that a cake of solidified melt isformed that fills substantially the space of the recess 19 and thusseals reliably and air tight the nozzle apertures 23. So that at thisstage the cover 18 does not receive too much heat from the nozzle plate10, said nozzle plate is lowered to a temperature just above thesolidification temperature of the melt material. Thus, the melt materialremaining within the channels 13 and the nozzles 14 cannot solidify, afeature that would significantly delay a later process of drawing offthe melt, since to this end the channels 13 and the nozzles 14 have tobe cleaned first of the solidified melt material. The temperature levelin the melter 1 remains virtually unmodified with respect to the processfor drawing off the melt.

FIG. 2 is a modified design of the melter of FIG. 1, and in particular adevice with two rows of nozzles 14. The melter 24 is elongated here inthe longitudinal direction and protected against temperature loss by theinsulating casing 25. The nozzle plate 26 is screwed here by means ofscrews 27 to the wall of the melter 24. For reasons relating tosimplifying the drawing, only one screw 27 is shown. The temperature ofthe nozzle plate 26 is measured by the temperature probe 28. The nozzleplate 26 is provided with channels 29 and cover 30 with channels 31,which provide in the manner described above for a suitable temperatureadjustment of the nozzle plate 26 and cover 30. The heating of themelter 24 is omitted here for the sake of simplifying the drawing.

The cover 30 has the recess, which is incorporated below the nozzles 14and serves here in the embodiment of FIG. 1 the purpose of accommodatinga residual melt material with the melt flow blocked off; then the meltcake solidifying in the recess 32 seals reliably the nozzles 14.

The Figure shows how the cover 30 is brought to the nozzle plate 26.This is done by means of a hinge 33, in which the arm 34 is positionedto which the nozzle plate 30 is attached. The ram 35, which serves thepurpose of pushing out a cake of solidified melt material located in therecess 32, is embedded in the cover 30. This is shown in FIG. 2 in theregion of the dashed-dotted drawing of the cover 30, which shows theposition of the cover 30 swivelled away from the nozzle plate 26. Theram 35 is drawn here in a pushed out position, caused by the pin 36. Inso doing, the ram 35 pushes the melt cake 37 out of recess.

It must also be pointed out that the heating or cooling channels shownin FIGS. 1 and 2, the latter in the region of the cover 18 or 30, canalso be replaced by any arbitrary heating medium, e.g. an electricheater. For the purpose of cooling, the heater must then be completelyswitched off, to which end there is also optionally a base cooling witha cooling medium.

We claim:
 1. Process for drawing off and blocking off a melt, inparticular of plastic material, with a heatable melter (1, 24), which isprovided with a blocking valve (3) and acts as a melt distributor andfrom which the melt flows into a nozzle plate (10, 26), which dividesthe melt by means of nozzles (14) into a plurality of strands, wherebythe temperature of the melter (1, 24) and nozzle plate (10, 26) are eachregulated separately, the blocking valve (3) is closable to block offthe melt and the nozzle plate (10, 26) is adapted to be tightly closedoff by a removable cover (18, 30), wherein to draw off the melt with theblocking valve (3) open, the temperature of the melter (1, 24) and thenozzle plate (10, 26) are kept at substantially the same level withrespect to each other, and to block off the melt with the blocking valve(3) closed, the nozzle plate (10, 26) is lowered to a temperature justabove the solidification temperature of the melt, and with the closureof the blocking valve (3) the cover (18, 30) cooled to a temperaturebelow the solidification temperature is laid on the nozzle plate (10,26) to overlie the nozzles, said cover defines a space into which aresidual melt flows and solidifies to form a plate-like seal of thenozzle apertures (23) while the melt in the nozzles is maintained in aliquid state.
 2. Device for carrying out a process for drawing off andblocking off a melt, in particular of plastic material, with a heatablemelter (1, 24), which is provided with a blocking valve (3) and acts asa melt distributor and to which is attached a nozzle plate (10, 26),which divides the melt by means of nozzles (14) having nozzle apertures(23) into a plurality of strands and which can be sealed off with anremovable cover (18, 30), wherein the nozzle plate (10, 26) and thecover (18, 30) are each provided with a separate and individuallycontrollable heating or cooling system (4, 17, 20, 29, 31) whereby thetemperature of each is independently regulated, and wherein the cover(18, 30) includes a recess (19, 32), extending over the nozzle apertures(23) when the cover is closed, as a collecting basin into which aresidual melt flows and is cooled and solidified to form a seal of allthe nozzle apertures without solidifying the melt in said nozzles. 3.Device, as claimed in claim 2, wherein the cover (18, 30) is providedwith a ram (35) penetrating the cover (18, 30) in the region of itsrecess (19, 23), in order to push out the solidified melt material. 4.Device, as claimed in claim 2, which further includes a temperatureinsulating layer (12) sealingly connected between the melter (1, 24) andthe nozzle plate (10, 26).